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I am confused how QNET VTOL (Vertical Take off & Landing) works, especially how pitch is changed and lift is generated.

I share a link of a relevant YouTube video and I am also sharing snaps of the top view and front side view of this trainer.

I am confused regarding a very basic question but I am not able to find its answer: according to my understanding here in this VTOL (Vertical Take off & Landing) trainer, a fan will act like the rotor of a helicopter (based upon the Bernoulli principle), and when this fan rotates with significant speed because of significant current provided to its motor, lift will be generated.

Please correct me if my understanding is not correct.

Top view enter image description here

Front side view enter image description here

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  • $\begingroup$ Related: electronics.stackexchange.com/questions/464317/… $\endgroup$
    – winny
    Oct 29, 2022 at 7:03
  • $\begingroup$ Being migrated to Aviation $\endgroup$
    – Russell McMahon
    Oct 29, 2022 at 10:55
  • $\begingroup$ You got itexactly right: Current can be applied to the Motor which starts spinning. Attached to the Motor is an airscrew (Propeller), which turns when the Motor turns. This Propeller generates a force which then pushes on the beam hence moving it up or down, exactly as you pointed out. Where lies the confusion? $\endgroup$
    – U_flow
    Nov 2, 2022 at 6:38
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    $\begingroup$ Also there may be a confusion here with use of 'pitch'. In the related question pitch refers to the angle of the beam holding the motor and fan. Not pitch of the blades like a true helicopter. There are only two wires going to the motor so it is a very simple cast plastic fan in the housing. So the lift is only controlled by the motor speed - recommend not over thinking this. $\endgroup$
    – GremlinWranger
    Nov 2, 2022 at 8:08
  • $\begingroup$ This device might be useful for teaching engineering concepts, but the "Verti-bird" I had as a kid was a better VTOL trainer: youtube.com/watch?v=FojzXSa6bxk $\endgroup$
    – Michael Hall
    Nov 2, 2022 at 22:44

2 Answers 2

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Your understanding is correct.

  • The motor is controlled by the input current.
  • When the motor and the attached propeller spins, lift is generated.
  • The lift counteracts the gravity and lifts the beam up.
  • The pitch angle of the beam is measured and used as an input to the control system.

Note that this is different from a helicopter: the primary means of changing the lift component in a helicopter is to collectively change the angle of attack of the rotor blades. The rotor's rotational speed is kept approximately constant.

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In such simple toys, it is not the pitch of the blades to be changed to control thrust rather the rotating speed of the fan via the power supplied to/from the electrical engine. Changing the pitch would be way to complicated and delicate (source):

rotor pitch change

The simple momentum theory allows us to go from the power generated by the engine to the thrust (thrust, not lift) generated by a rotor/propeller:

$ T = \sqrt[3]{2 \rho A P^2} $

where $A$ is the rotor area, $\rho$ is the density and $P$ the power needed to spin the rotor.

For an electrical engine the power is simply $P=V\cdot I$ times an efficiency factor $\eta$.

The fan in the picture is ducted so that we can assume some 30% thrust increment the power being the same.

The thrust equals and is opposite to the weight of the arm+propeller assembly.

Knowing engine ratings, weights and disk area it is possible to do the calculation. If you know these values I might complete my answer with real numbers.

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